U.S. Pat. No. 6,641,377 B2 discloses a linear compressor having a pump chamber, in which a piston may effect reciprocating motion, a frame connected firmly to the pump chamber, on which frame an oscillating body connected to the piston is held via at least one spring so as to be able to effect reciprocating motion, and at least one electromagnet mounted on the frame for driving the reciprocating motion of the oscillating body.
The oscillatory force exerted by the magnet on the oscillating body brings about a corresponding oscillatory counterforce, which the frame exerts on a mount to which it is fixed. If not compensated, this oscillatory counterforce may cause the mount or other components connected thereto to oscillate, which will be perceived by a user as operating noise.
To keep such oscillations small, in the known linear compressor two pistons work together, penetrating into the pump chamber from two different sides. If these pistons have identical masses and are supported by springs of identical strength, it is possible to control the driving electromagnet of each piston in such a way that the pistons oscillate exactly in phase opposition, such that the counterforces caused by the oscillatory motion and acting on the frame compensate one another.
Such a linear compressor is complex, since the pistons and the drive means associated therewith have in each case to be duplicated. However, it is also difficult to ensure precisely mirror-symmetrical movement of the two pistons, since production-determined variance of the oscillating masses and in particular of the stiffness of the springs supporting them may lead to different natural frequencies of the two pistons. This may, if the magnets are excited with the same alternating current on both sides, result in the piston movement exhibiting different amplitudes and phases.
It is also possible to construct a linear compressor with a single oscillatory piston, in which the transmission of counterforces exerted on a frame to a mount of the compressor is restricted in that the frame is for its part suspended in an oscillatory manner relative to the mount, but such a linear compressor requires a large number of springs, which make assembly of the linear compressor time-consuming and costly.
A further problem with a sprung mount is that most types of spring, if arranged in order to counteract a movement of the frame parallel to the direction of oscillation of the oscillating body, are easily deformable transversely of this direction, such that the frame may be caused to effect rolling movements of considerable amplitude, unless these are suppressed by additional springs providing lateral support or by a rail guide.